Wafer transport apparatus for ion implantation apparatus

ABSTRACT

A wafer transport apparatus for an ion implantation apparatus includes means for successively transferring wafers from a wafer cassette, inserting the wafers into an auxiliary vacuum chamber, transferring the wafers into a specific position within a vacuum processing chamber, transferring a wafer from that position to a position for ion implanation processing while at the same time transferring a processed wafer to a second position within the vacuum processing chamber, with the wafers being held retained during this transfer, successively transferring the processed wafers into a second auxiliary vacuum chamber, and transporting the wafers from the second auxiliary vacuum chamber to be inserted into a cassette, e.g. the cassette from which the wafers were originally removed. The wafers are supported or held retained by the transfer and transport means during the entire process, so that problems resulting from gravity feed of wafers along inclined surfaces, which arise with prior art apparatus of this type, are eliminated.

This application is a continuation of application Ser. No. 848,567,filed on Apr. 7, 1986, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a wafer transport apparatus for use inan ion implantation apparatus which performs ion implantation processingof wafers of material utilized to manufacture semiconductor devices,e.g. wafers of crystalline silicon (referred to in the followingspecification and claims simply as "wafers"). As is well known an ionimplantation apparatus includes means for transporting wafers from theexternal atmosphere into an auxiliary vacuum chamber, and from thereinto a vacuum processing chamber in which ion implantation is performed.The wafers are then transferred from the vacuum processing chamber backto the auxiliary vacuum chamber and from there back out into theatmosphere. With prior art types of wafer transport apparatus for suchan application, the weight of each wafer is employed to provide themotive force for this transportation, i.e. the force of gravity actingon each wafer is employed to slide the wafer along downwardly slopingsurfaces. More specifically, such a prior art wafer transport apparatuscomprises first inclined surface guidance means for transporting wafersfrom the external atmosphere into an auxiliary vacuum chamber, and fromthere into a vacuum processing chamber, together with second inclinedsurface guidance means, separate from the firs surface guidance means,for transferring the wafers from the vacuum processing chamber, throughan auxiliary vacuum chamber, back to the external atmosphere. The wafersare successively moved downward as they slide along the inclinedguidance surfaces, to be thereby successively transported to requisitepositions.

Such a prior art wafer transport apparatus has the advantage that nodrive apparatus is required. However it presents the following problems.Firstly, if a layer of photo-resist has been formed on each wafer, thensticking of the wafers may occur during the gravity transportationprocess, causing interruptions in production. Furthermore, the wafersmay adhere to stopper members which are provided in the inclined surfaceguidance means. This problem can occur even with wafers which do nothave a layer of photo-resist formed thereon. In addition, impact of thewafers against the stopper members results in the formation andaccumulation of small wafer particles, resulting in build-up of dust,and also causes damage to the wafers.

Furthermore with such a prior art wafer transport apparatus, problemsarise with regard to sequential transfer of wafers from a wafer cassetteto an ion implantation processing section, and subsequent transfer ofwafers from the ion implantation processing section to be loaded into awafer cassette. Due to the above reasons, prior art types of wafertransport apparatus present serious problems with regard to productionefficiency.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the disadvantagesof such a prior art type of wafer transport apparatus for use in an ionimplantation apparatus.

In a first aspect, the present invention comprises a wafer transportapparatus for an ion implantation apparatus whereby wafers aretransferred from a first auxiliary vacuum chamber to the interior of avacuum processing chamber, and from the interior of the vacuumprocessing chamber to a second auxiliary vacuum chamber, respectively,by two drive means acting on a wafer transfer mechanism in a mutuallysynchronized manner.

In a second aspect, the present invention comprises a wafer transportapparatus for an ion implantation apparatus which incorporates a novelwafer transporting system whereby wafers are successively removed from awafer cassette and are subsequently successively reloaded within thesame cassette, following ion implantation processing.

More specifically, the present invention relates to a wafer transportapparatus for use in an ion implantation apparatus having a vacuumprocessing chamber containing ion implantation processing means,comprising:

first and second auxiliary vacuum chambers;

first wafer transfer means for transferring a wafer between said firstauxiliary vacuum chamber and a first predetermined position within saidvacuum processing chamber;

second wafer transfer means for transferring a wafer between said secondauxiliary vacuum chamber and a second predetermined position within saidvacuum processing chamber, and;

wafer retaining and transporting means for transferring two waferswithin said vacuum processing chamber in a releasably retainedcondition, being operable to retain and transfer said two wafers betweena third predetermined position within said vacuum processing chamber atwhich said ion implantation processing is performed and said first andsecond predetermined positions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an oblique external view of an ion implantation apparatusincorporating an embodiment of a wafer transport apparatus according tothe present invention;

FIG. 2 is a general plan view of the interior of a vacuum processingchamber in the ion implantation apparatus of FIG. 1;

FIG. 3 is a cross-sectional view in elevation to illustrate the interiorof the vacuum processing chamber and of two auxiliary vacuum chambers ofthe ion implantation apparatus of FIG. 1, showing a pair of wafertransfer units in a raised condition, and;

FIG. 4 is a cross-sectional view corresponding to FIG. 3, showing thepair of wafer transfer units in a lowered condition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described, referringto FIGS. 1 through 4, in which corresponding components are designatedby identical reference numerals. FIG. 1 is an oblique external view ofan ion implantation apparatus incorporating an embodiment of a wafertransport apparatus according to the present invention, in which wafersare designated as W. Reference numerals 10 and 12 denote wafer cassettesupporting stages mounted on respective elevating units 14 and 16, uponwhich are placed respective wafer cassettes each containing a pluralityof wafers to be subjected to ion implantation processing. One of suchwafer cassettes, designated as 11, is shown positioned upon wafercassette mounting stage 10. Each of the elevating units 14 and 16 isoperable to elevate or lower a wafer cassette supported thereon, bycontrolled amounts for bringing the wafer cassette to a requisitevertical position. The apparatus further includes wafer transport units18 and 20, a wafer alignment unit 22, first and second auxiliary vacuumchambers 24 and 26, and a vacuum processing chamber 28.

As shown, a plurality of wafers are vertically stacked within the wafercassette 11, each of which can be brought to a desired vertical positionby operation of the elevating unit 14, for successive removal of wafersfrom wafer cassette 11 by the wafer transport unit 18 and for subsequentreloading of the wafers into specific positions in wafer cassette 11 bywafer transport unit 18 following ion implantation processing of thewafers, as described hereinafter. Although not shown in FIG. 1, a secondwafer cassette can be placed upon wafer cassette supporting stage 12,mounted on elevating unit 16, and can be raised or lowered to specificpositions as required for successive removal of wafers therefrom andsubsequent reloading of the wafers thereof following ion implantationprocessing of the wafers, by operation of elevating unit 16.

The wafer transport unit 18 includes a wafer carrier member 40, andincludes a drive mechanism which is operable to rotate wafer carriermember 40 in a horizontal plane about a fixed axis and to horizontallyextend and retract wafer carrier member 40 radially with respect to thataxis of rotation. One function of the wafer transport unit 18 is toremove wafers from wafer cassette 11 and to reload wafers into wafercassette 11. Removal of a specific wafer is performed first by elevatingunit 14 acting to raise wafer cassette 11 to a specific height, suchthat the lower face of a requisite wafer is slightly higher than theupper face of wafer carrier member 40, then by rotation of wafer carriermember 40 until one end thereof is positioned opposite the requiredwafer. The wafer carrier member 40 is then moved radially outward, tobecome positioned below the requisite wafer, whereupon elevating unit 14acts to slightly lower the wafer cassette 11, leaving the requisitewafer supported upon wafer carrier member 40. The wafer carrier member40 is then moved radially inward towards the axis of rotation thereof,carrying the requisite wafer out of wafer cassette 11.

To load a wafer into the wafer cassette 11, an opposite sequence ofoperations is performed. First, wafer cassette 11 is set to a specificvertical height by elevating unit 14. Next, wafer carrier member 40,carrying the requisite wafer at one end thereof, is rotated until thatend is positioned opposite to wafer cassette 11, and is then movedradially outward to carry the wafer into a specific vertical positionwithin wafer cassette 11. The wafer cassette 11 is then slightlylowered, to leave the requisite wafer supported therewithin, whereuponwafer carrier member 40 is moved radially inward, out of wafer cassette11.

It should be noted that it would also be possible to perform the aboverotation and extension/retraction operations of wafer carrier member 40in a substantially simultaneous manner. However it would be necessary inthis case to arrange the timings of rotational and linear movement ofwafer carrier member 40 such as to avoid the possibility of obstructionto that movement occurring.

Furthermore, in the above description it is assumed that only the wafercassette 11 is selectively raised and lowered in the process ofperforming removal of a wafer therefrom or loading a wafer therein.However it would be equally possible to provide elevating means in wafertransport unit 18, for producing slight amounts of vertical movement ofwafer carrier member 40 to implement lifting of a wafer in wafercassette 11 to become supported on wafer carrier member 40, for removalof a wafer from wafer cassette 11, or lowering of a wafer from wafercarrier member 40 to be left supported within wafer cassette 11, forloading a wafer in wafer cassette 11 as described above.

The operation of wafer transport unit 20, for removing a wafer from awafer cassette positioned on supporting stage 12, is identical to thatdescribed above with respect to wafer cassette 11, and furtherdescription will be omitted.

The wafer transport unit 18 also has the functions of transferringwafers to and from the wafer alignment unit 22, transferring wafers tothe interior of auxiliary vacuum chamber 24 and removing wafers from theinterior of auxiliary vacuum chamber 24. Similarly, wafer transport unit20 has the functions of transferring wafers to and from the waferalignment unit 22, removing wafers from the interior of auxiliary vacuumchamber 26, and transferring wafers to the interior of auxiliary vacuumchamber 26. The wafer alignment unit 22 functions to detect a specificperipheral edge portion of a wafer which is placed thereon, by wafertransport unit 18 or 20, and to rotate the wafer, in a horizontal plane,into a specific orientation. To perform these functions, wafer alignmentunit 22 includes a wafer supporting stage (disposed below a wafer W, andnot visible in FIG. 1), which is rotatable, and also incorporates anedge detection unit 44 which can include for example a pair ofphoto-sensors. After a wafer has been transferred by wafer transportunit 18 or 20 onto the supporting stage of wafer alignment unit 22 andhas been rotated thereby into a specific orientation, the wafer is thentransferred to the interior of either auxiliary vacuum chamber 24 or 26,as described hereinafter.

The auxiliary vacuum chamber 24 can be hermetically sealed from theouter atmosphere or opened to that atmosphere, by closing or opening anouter gate 30. Similarly, the auxiliary vacuum chamber 26 can behermetically sealed from the outer atmosphere or opened to thatatmosphere, by closing or opening an outer gate 32. Reference numerals33 and 34 denote covers which contain actuating mechanisms forperforming various functions within the interiors of auxiliary vacuumchambers 24 and 26 respectively, e.g. valves, etc. Reference numerals 35and 36 respectively denote viewing windows which are opticallytransparent and are provided in the exterior walls of auxiliary vacuumchambers 24 and 26 respectively. Reference numerals 46 and 47 denotedrive units of the wafer transport units 18 and 20 respectively, fordriving the wafer carrier members 40 and 42 respectively for rotationand radial extension and retraction, as described hereinabove. Referencenumerals 48 and 49 denote upper cover plates of wafer transport units 18and 20 respectively. The upper face of each of the cover plates 48 and49 is positioned below the upper face of each of the wafer carriermembers 40 and 42.

Wafer transfer operation external to the auxiliary vacuum chambers 24and 26 is performed as follows. It will be assumed that a wafer in wafercassette 11 is to be subjected to ion implantation, and that this waferhas been positioned at an appropriate height from removal from wafercassette 11 by wafer transport unit 18. The wafer carrier member 40 isfirst rotated until one end thereof is positioned opposite wafercassette 11, then is moved radially outwards (or is rotated while beingmoved radially outward) to a position below the wafer, and then removesthe wafer from wafer cassette 11 as described hereinabove. The wafercarrier member 40 is then moved radially inward, then is rotated untilthe end thereof upon which the wafer is carried becomes positionedopposite wafer alignment unit 22, whereupon it is moved radially outwardto leave the wafer supported on the supporting stage of wafer alignmentunit 22. The wafer carrier member 40 is then again rotated, as the firststage in removing a second wafer from wafer cassette 11. The waferalignment unit 22 then rotates the wafer supported thereon, into aspecific orientation as described hereinabove. When this orientation iscompleted, wafer transport unit 20 moves the wafer carrier member 42thereof radially outward to lift the wafer from wafer alignment unit 22,then moves wafer carrier member 42 radially inward and rotates themember until the end thereof which carries the wafer becomes positionedopposite outer gate 32 of auxiliary vacuum chamber 26. At this point,outer gate 32 is in the open state, and wafer carrier member 42 is thenmoved radially outward to insert the wafer into the interior ofauxiliary vacuum chamber 26.

Subsequently, outer gate 32 closes, and the wafer which has beentransferred therein is subjected to ion implantation within vacuumprocessing chamber 28 and transferred to auxiliary vacuum chamber 24, asdescribed hereinafter. Outer gate 30 of auxiliary vacuum chamber 24 thenopens, and wafer transport unit 18 then operates wafer carrier member 40to remove this wafer from auxiliary vacuum chamber 24, and transportsthe wafer to a specific position within wafer cassette 11, by theloading operation described hereinabove. The wafer may for example bereplaced in its original position within wafer cassette 11.

It can be understood from the above that the wafer transport unit 18, inaddition to transporting wafers (prior to ion implantation) from thewafer cassette 11 to the wafer alignment unit 22, also serves totransport wafers (following ion implantation) from the auxiliary vacuumchamber 24 back into wafer cassette 11. In order to perform these twotypes of operation with maximum efficiency, it is possible to arrangefor example that wafer transport unit transfers a wafer (prior to ionimplantation) to the wafer alignment unit 22, then moves wafer carriermember 40 to transfer a wafer (following ion implantation) fromauxiliary vacuum chamber 24 to be loaded into wafer cassette 11, thenremoves another wafer (prior to ion implantation) from wafer cassette11, transfers that wafer to wafer alignment unit 22, and so on,repetitively.

With the present embodiment, while wafers are being successively removedfrom wafer cassette 11 mounted on supporting stage 10, it can be seenthat wafers move successively in a path leading from wafer cassette 11,to wafer transport unit 18, to wafer alignment unit 22, to wafertransport unit 20, to auxiliary vacuum chamber 26, to vacuum processingchamber 28 for ion implantation processing, to auxiliary vacuum chamber24, to wafer transport unit 18, then back into wafer cassette 11. Duringthis processing of successive wafers of wafer cassette 11, another wafercassette can be prepared, and set upon wafer cassette supporting stage12. When all of the wafers of wafer cassette 11 have been processed, itis removed from supporting stage 10, to be replaced by another cassette.During this changeover interval, processing of the wafer cassettepositioned on wafer cassette supporting stage 12 is initiated. Theapparatus is now set to operate with a different processing flow pathfrom that described above. Specifically, a wafer is removed from thewafer cassette on supporting stage 12, then is moved to wafer transportunit 20, to wafer alignment unit 22, to wafer transport unit 18, toauxiliary vacuum chamber 24, to vacuum processing chamber 28 for ionimplantation processing, to auxiliary vacuum chamber 26, to wafertransport unit 20, then back into the wafer cassette on supporting stage12. In this way, no production time is lost during the changeover ofwafer cassettes on supporting stages 11 and 12, as the cassettessuccessively become completely processed and are replaced by othercassettes. It can therefore be understood that such an apparatusprovides a very high level of production efficiency, with minimum wasteof production time.

When all of the wafers of the wafer cassette positioned on stage 12 havebeen completely processed by ion implantation, the wafer cassette isreplaced upon supporting stage 12 by another wafer cassette, and thewafers therein are then successively processed as described above. Asstated previously, processing of wafers from a wafer cassette positionedon wafer cassette supporting stage 12 is performed during the changeoverof wafer cassettes on supporting stage 10. Subsequently, upon completionof processing of the wafers of the wafer cassette on supporting stage12, changeover of this wafer cassette is carried out. During thischangeover, processing of the wafers in the wafer cassette on supportingstage 10 is performed.

FIG. 2 is a general plan view of the interior region of vacuumprocessing chamber 28 in which ion implantation is performed, forassistance in describing the manner of transferring wafers within thatchamber. FIG. 3 is a general cross-sectional view in elevation, showingthe interior of vacuum processing chamber 28, and auxiliary vacuumchambers 24 and 26 in a condition in which each auxiliary vacuum chambercommunicates with the vacuum processing chamber 28. FIG. 4 is across-sectional view corresponding to FIG. 3, showing a condition inwhich auxiliary vacuum chambers 24 and 26 are hermetically sealed withrespect to vacuum processing chamber 28. In FIGS. 2 to 4, referencenumeral 52 denotes a wafer retaining and transferring mechanism whichserves to transfer wafers successively from a leftward position invacuum processing chamber 28 (as seen in FIG. 2) to an ion implantationposition, and then to a rightward position in vacuum processing chamber28, or to transfer wafers from the rightward position, to the ionimplantation position, then to the leftward position. The waferretaining and transferring mechanism 52 includes two wafer retainingmembers 52A and 52B, respectively provided with arms 52A-1, 52A-2, and52B-1, 52B-2. Arms 52A-1 and 52A-2 can be positioned to retaininglysupport the left-hand sides (as viewed in FIGS. 2 to 4) of two wafersrespectively, for example the wafers designated as W1 and W2 in FIG. 2.Arms 52B-1 and 52B-2 can be positioned to retainingly support theright-hand sides of the latter two wafers respectively. The waferretaining members 52A and 52B are respectively driven for horizontallinear movement (i.e. from right to left and from left to right, as seenin FIGS. 2 to 4) in a mutually synchronized manner, by drive units 54and 56, each of which can include for example a stepping motor or a DCbrushless motor, and a drive belt for coupling the motor to thecorresponding wafer retaining member. Each of the arms 52A-1, 52A-2,52B-1, 52B-2 of the wafer retaining members 52A and 52B is formed with aportion on one side thereof having an arc-shaped profile (as viewed inplan, in FIG. 2). Each of these arm side portions is formed to have asubstantially L-shaped cross-sectional shape, as seen in FIGS. 3 and 4,whereby an arc-shaped horizontal ledge surface and vertical side surfaceis formed in each of these arc-shaped side portions, for respectivelyperforming wafer supporting and wafer retaining functions as describedhereinafter.

Reference numerals 65 and 75 denote wafer transfer units forrespectively transferring wafers from auxiliary vacuum chamber 26 to theinterior of vacuum processing chamber 28 and from auxiliary vacuumchamber 24 to the interior of vacuum processing chamber 28, by executingcontrol upward and downward movement of platens 60 and 70 as describedhereinafter. In the following description of the operation of waferretaining and transferring mechanism 52, based on FIGS. 2 and 3 butassuming that a clamp member 84 has been set in the open state asdescribed hereinafter, it is assumed that one wafer (W1) has just beentransferred from auxiliary vacuum chamber 26 onto platen 60, whileanother wafer (W2) has just completed ion implantation processing, sothat wafer W1 has to be transferred to the central ion implantationposition and wafer W2 has to be transferred to the leftward position(below auxiliary vacuum chamber 24). In this condition, the horizontalarc-shaped shelf portions of each of arms 52A-1 to 52B-2 is positionedslightly below the lower faces of wafers W2 and W1, which are mutuallypositioned substantially in the same horizontal plane. The operation ofwafer retaining and transferring mechanism 52 then is as follows. First,wafer retaining member 52A is driven to move slightly to the right,while wafer retaining member 52B is moved slightly to the left, by asufficient amount to lightly clamp opposing edge portions of wafer W1between the arc-shaped vertical surface portions of arms 52A-2 and52B-2, and to similarly lightly clamp wafer W2 between the arc-shapedvertical surface portions of arms 52A-1 and 52B-1. The wafer retainingmembers 52A and 52B are then moved upward (or platens 60 and 80 aremoved downward) by a sufficient amount to permit movement above platens60 and 80 by wafer retaining members 52A and 52B. The wafer retainingmembers 52A and 52B are then moved together towards the left, carryingwafers W2 and W1, until the positions indicated by the broken-lineoutlines in FIG. 2 are reached. The wafer retaining member 52A is thenmoved slightly to the left, and wafer retaining member 52B is movedslightly to the right, by a sufficient amount to release the lightlyclamped conditions of wafers W1 and W2, but leaving the wafers supportedupon the horizontal arc-shaped shelf portions of arms 52A-1 to 52B-2.The wafer retaining members 52A and 52B are then move downward (orplatens 70 and 80 are raised) by a sufficient amount to leave wafers W1and W2 respectively supported on platens 70 and 80.

In this way, wafer W1 has been transferred to the position in vacuumprocessing chamber 28 at which it can be subjected to ion implantation(after rotational movement as described hereinafter), while wafer W2 hasbeen transferred to platen 70 of wafer transfer unit 74, and can now betransferred into auxiliary vacuum chamber 24 by wafer transfer unit 74.

It will be apparent that transfer of wafers in the opposite direction tothat described above, by operation of wafer retaining members 52A and52B, can be performed in a similar manner to that described above. Itcan be understood from the above description that the manner ofoperation of wafer retaining and transferring mechanism 52 is similar tothat of a shuttle.

The wafer platens 60, 70 and 80 are replaceable components, which can beselected in accordance with the size and shape of wafers which are to beprocessed. The wafer platen 60 is mounted on a member 62 which functionsas an inner gate, to provide hermetic sealing between auxiliary vacuumchamber 26 and the interior of vacuum processing chamber 28 when set inan upward position thereof, as shown in FIG. 4, and to providecommunication between auxiliary vacuum chamber 26 and the interior ofvacuum processing chamber 28 when set in a downward position, as shownin FIG. 3. The inner gate 62 is raised and lowered by an elevating unit64, which can be of hydraulic, pneumatic or electrical operation. Theoperation of elevating unit 64 is controlled by a control unit (notshown in the drawings). The inner gate 62, with elevating unit 64,platen 62 and the associated control unit, constitutes a wafer transferunit 65.

Similarly, as shown at the left side of FIGS. 3 and 4, an inner gate 72can be raised to provide hermetic sealing between auxiliary vacuumchamber 24 and the interior of vacuum processing chamber 28, andsupports wafer platen 70. Controlled raising and lowering of inner gate72 and wafer platen 70 is performed by an elevating unit 74 and anassociated control unit (not shown in the drawings). The inner gate 72,with platen 70, elevating unit 74 and the associated control unitconstitute a wafer transfer unit 75.

Reference numeral 58 in FIGS. 2 to 4 denotes an ion implantationprocessing positioning system, which includes wafer platen 80, a platen82 for supporting wafer platen 80, a wafer clamp member 84, and a shaft86 to which wafer clamp member 84 is fixedly attached, together with amotor 90 which is disposed external to vacuum processing chamber 28 andis coupled to rotate the wafer clamp member 84 through such means as anelectrical sealed bearing 88, an actuating member 93 which bears againsta lower face of platen 82, and a drive unit 94 for raising or loweringthe actuating member 93. The processing positioning system 58 furtherincludes means for cooling the interior of platen 82, to absorb heatwhich is generated by the ion implantation process. This is accomplishedby forming platen 82 with a hollow interior, and circulating a coolantmedium through this interior, the coolant being passed inward andoutward through tubes 92. Numeral 96 indicates the direction of incidentions within vacuum processing chamber 28.

The operation of the processing positioning system 58 is as follows.Prior to transferring a wafer onto wafer platen 80, the platen is set inthe position shown in FIGS. 3 and 4, by operation of drive unit 94 andactuating member 93, whereupon the wafer clamp member 84 is raise upwardfrom the wafer that is currently supported upon wafer platen 80, byrotation of shaft 86 by motor 90. Transfer of another wafer onto waferplaten 80 is then carried out as described hereinabove, by operation ofwafer retaining and transferring mechanism 52, and then motor 90operates to rotate shaft 86 in the opposite direction, to thereby movewafer clamp member 84 downward to clamp the wafer between wafer clampmember 84 and wafer platen 80. Drive unit 94 then operates to driveactuating member 93 upward, to thereby rotate the clamped wafer aboutthe axis of rotation of shaft 86, until the wafer has been moved intothe appropriate position for ion implantation by incident ions 96. Uponcompletion of ion implantation, the above sequence of operations isreversed, to leave the wafer in the position indicated for W2 in FIG. 3.

In FIG. 4, both of the wafer transfer units 65 and 75 are shown in therespective upward positions thereof, whereby the auxiliary vacuumchambers 26 and 24 are hermetically sealed from the interior of vacuumprocessing chamber 28.

It should be noted at this point that, although it is preferable thatthe outer gates 30 and 32 and also the wafer transfer units 65 and 75operate in a mutually synchronized manner, this is not essential to thepresent invention.

The overall operation of vacuum processing chamber 28 and of wafertransport through that chamber and auxiliary vacuum chambers 24 and 26will now be described, referring to FIGS. 2 to 4. It should be notedthat the following description is only given by way of example, and thatthe mode of operation of the present invention is not limited thereto.For ease of understanding, it will be assumed that the first wafer fromwafer cassette 11 has been transported into auxiliary vacuum chamber 26,by respective operations of wafer transport unit 18, wafer alignmentunit 22, and wafer transport unit 20. At this stage, both of the wafertransfer units 65 and 75 are in the raised condition as shown in FIG. 4,so that the auxiliary vacuum chambers 26 and 24 are hermetically sealedwith respect to vacuum processing chamber 28 and both of the outer gates30 and 32 are open. In this condition, the interiors of auxiliary vacuumchambers 26 and 24 are preferably filled with an inert gas such asnitrogen, at atmospheric pressure. The outer gates 32 and 30 are nowclosed, and the auxiliary vacuum chambers 26 and 24 are respectivelyevacuated to a specific pressure, for example to 10⁻² Torr. When this iscompleted, the wafer transfer units 65 and 75 are lowered to thespecific positions shown in FIG. 3, thereby setting both of theauxiliary vacuum chambers 24 and 26 in communication with the interiorof vacuum processing chamber 28, which is held at a fixed level ofvacuum, for example at 10⁻⁶ Torr. The first wafer is now transferred bywafer retaining and transferring mechanism 52 to the central position inprocessing positioning system 58, i.e. the position of wafer W2 in FIG.2, with wafer retaining and transferring mechanism 52 moving leftwardinto the position indicated by the broken-line outline in FIG. 2. Thewafer is then released from the retained condition by wafer retainingand transferring mechanism 52 as described hereinabove, to betransferred onto platen 80, whereupon wafer retaining and transferringmechanism 52 returns to the rightward position thereof (indicated by thefull-line outline in FIG. 2). The wafer transfer unit 65 is then raisedto the upward position thereof as shown in FIG. 4, to therebyhermetically seal auxiliary vacuum chamber 26 from vacuum processingchamber 28, whereupon outer gate 32 is opened and a second wafer fromthe wafer cassette is inserted into auxiliary vacuum chamber 26, tobecome supported on wafer platen 60 of wafer transfer unit 65. The outergate 32 is then closed, and the interior of auxiliary vacuum chamber 26is evacuated to the pressure level described above.

Prior to transfer of the first wafer onto platen 80, the wafer carrierclamp 84 is raised to the open condition, and is then lowered to clampthe wafer against platen 80 when this transfer has been completed. Thefirst wafer is then moved to the ion implantation position by operationof actuating member 93. On completion of implantation processing, thefirst wafer is returned to the position shown in FIG. 3, and the clampmember 84 is raised to release the wafer.

Upon completion of ion implantation processing of the first wafer (forexample, during the time interval in which the first wafer is beingunclamped and restored to the position W2 shown in FIG. 3), the secondwafer from the wafer cassette on unit 65 is lowered into the positionshown for wafer W1 in FIG. 3. The first and second wafers are thenrespectively transferred by wafer retaining and transferring mechanism52 onto wafer platens 70 and 80, leaving wafer retaining andtransferring mechanism 52 in the position indicated by the broken-lineoutline in FIG. 2. The wafer transfer units 65 and 75 are now raisedinto the upward positions shown in FIG. 4.

While ion implantation processing of the second wafer is taking place,the third wafer from the wafer cassette on supporting stage 10 istransported into auxiliary vacuum chamber 26, while the first wafer istransferred out of auxiliary vacuum chamber 24, to be then reloaded intothe wafer cassette.

Subsequent operations to process the remaining wafers of the wafercassette on supporting stage 10 are simply repetitions of thosedescribed above. It can be understood that by appropriately mutuallylinking the timings of operations by the wafer transfer units 65 and 75,outer gates 30 and 32, and processing positioning system 58 inconjunction with the wafer transport units 18 and 20, a smooth and rapidflow of wafers from a wafer cassette, through ion implantationprocessing, and back into the wafer cassette, can be easily achieved.

In the above embodiment, a pair of wafer cassette supporting stages 10and 12 are provided, at the right and left sides of the apparatus, withwafers from a wafer cassette on one of these supporting stages beingprocessed while exchange of wafer cassettes on the other supportingstage is being carried out. However the present invention is not limitedto this number of wafer cassette supporting stages, or to the describedpositions for these supporting stages. For example, both wafer cassettesupporting stages may be positioned at the front of the apparatus.Furthermore, since the rate of processing of wafers within vacuumprocessing chamber 28 can be made extremely high, due to the manner ofoperation of an apparatus according to the present invention, it ispossible that an increased rate of productivity can be achieved byemploying a greater number of wafer cassette supporting stages, forexample four supporting stages.

Alternatively, if means are provided for exchanging successive wafercassettes at a sufficiently high speed, so that the time required toexchange cassettes on a supporting stage is not a limiting factor, thenit would be possible to employ only a single wafer cassette supportingstage, e.g. supporting stage 10. In this case the apparatus would be asdescribed for the preferred embodiment, but with the omission ofsupporting stage 12 and elevating unit 16, and with only a single flowpath of wafers through the apparatus being employed.

With the present invention, as described hereinabove, a wafer istransferred from an auxiliary vacuum chamber into a vacuum processingchamber, is subjected to ion implantation processing therein, and isthen transferred to a second auxiliary vacuum chamber. Such a systemenables successive transfers of wafers into and out of the vacuumprocessing chamber to be carried out in a very smooth and efficientmanner, and also enables wafers to be successively removed from a wafercassette, processed by ion implantation, then loaded back into the wafercassette, by successive cyclically repeated operations. As a result,maximum wafer transfer speed can be attained using a minimum of systemcomponents. Furthermore, the wafers are not subjected to impact duringany stage of transportation within the apparatus. This results in theelimination of the problems of dust particle accumulation and of damageto wafers which arise with prior art types of such apparatus that employsliding of wafers along inclined surfaces under the force of gravity,and impacts against stopper members, for wafer transfer. In addition theproblems of wafers sticking within the transportation path, which arisewith such prior art types of apparatus employing the force of gravityacting on the wafers, are eliminated.

Furthermore, since the time required to perform ion implantationprocessing of each wafer is quite short, and since the present inventionenables extremely rapid transfer of wafers through the apparatus, ahigher rate of processing can be achieved than has been possible in theprior art. Maximum advantage of this high processing rate can beattained, as described above, by using a greater number of wafercassette supporting stages, e.g. four supporting stages. In this way,during processing of wafers from one cassette, exchange of a pluralityof other cassettes on different wafer cassette supporting stages cantake place, i.e. replacement of wafer cassettes containing wafers whichhave been completely processed with wafer cassettes containing wafers tobe processed.

Although the present invention has been described in the above withreference to a specific embodiment, it should be noted that variouschanges and modifications to the embodiment may be envisaged, which fallwithin the scope claimed for the invention as set out in the appendedclaims. The above specification should therefore be interpreted in adescriptive and not in a limiting sense.

What is claimed is:
 1. An ion implantation apparatus, comprising:avacuum processing chamber in which a wafer is subjected to ionimplantation processing; first and second auxiliary vacuum chambers eachof which is hermetically sealable from or connectable to the outeratmosphere and vacuum processing chamber, and each of which isconstructed to temporarily store the water; first wafer transfer meansfor transferring a wafer into the vacuum processing chamber from thefirst auxiliary vacuum chamber; second wafer transfer means fortransferring the wafer to the second auxiliary vacuum chamber from thevacuum processing chamber; driving means for driving the first andsecond wafer transfer means in a mutually synchronized manner; wafercassette supporting means for supporting a cassette containing aplurality of wafers; and wafer transport means for transporting thewafer into the first auxiliary vacuum chamber from the cassette one byone; said driving means being connected to the first and second wafertransfer means to move them at the same time so that two wafers aresimultaneously transferred to the vacuum processing chamber and secondauxiliary vacuum chamber from the first auxiliary vacuum chamber andvacuum processing chamber; wherein said first wafer transfer meansincludes first and second arms, said second wafer transfer meansincludes third and fourth arms, and said driving means includes a firstretaining member connecting the first and third arms together, and asecond retaining member connecting the second and fourth arms together.2. The apparatus according to claim 1, wherein said first, second,third, and fourth arms are arranged in parallel with one another, andsaid first retaining member has opposite ends connected to the first andsecond arms, and said second retaining member has opposite endsconnected to the second and fourth arms, the first and second retainingmembers linearly moving in a parallel state.
 3. An ion implantationapparatus, comprising;a vacuum processing chamber in which a wafer issubjected to ion implantation processing; first and second auxiliaryvacuum chamber each of which is hermetically sealable from orconnectable to the outer atmosphere and vacuum processing chamber, andeach of which is constructed to temporarily store the wafer; first wafertransfer means for transferring a wafer into the vacuum processingchamber from the first auxiliary vacuum chamber; second wafer transfermeans for transferring the wafer to the second auxiliary vacuum chamberfrom the vacuum processing chamber; driving means for driving the firstand second wafer transfer means in a mutually synchronized manner; wafercassette supporting means for supporting a cassette containing aplurality of wafers; and wafer transport means for transporting thewafer into the first auxiliary vacuum chamber from the cassette one byone; said first wafer transfer means including first and second arms;said second wafer transfer means including third and fourth arms; saiddriving means moving said first and second arms so that a first waferbecomes retained therebetween and moves said third and fourth arms sothat a second wafer becomes retained therebetween; wherein said firstand third arms are fixedly connected to said first wafer transfer meansand said second and fourth arms are fixedly connected to said secondwafer transfer means, said driving means being operable to selectively;(a) drive said first and second wafer retaining members in firstmutually opposite directions, for retaining said first wafer betweensaid first and second arms and retaining said second wafer between saidthird and fourth arms; (b) drive said first and second wafer retainingmembers together along a specific direction, for transferring one ofsaid first and second wafers from said first auxiliary vacuum chamber tosaid vacuum processing chamber while transferring the other wafer ofsaid first and second wafers from said vacuum processing chamber to saidsecond auxiliary vacuum chamber; (c) drive said first and second waferretaining members in second mutually opposite directions, for releasingsaid first wafer from between said first and second arms and releasingsaid second wafer from between said third and fourth arms; and (d) drivesaid first and second wafer retaining members together in the oppositedirection to said specific direction.
 4. An ion implantation apparatus,comprising:a vacuum processing chamber in which a wafer is subjected toion implantation processing; first and second auxiliary vacuum chamberseach of which is hermetically sealable from or connectable to the outeratmosphere and vacuum processing chamber, and each of which isconstructed to temporarily store the wafer; first wafer transfer meansfor transferring a wafer into the vacuum processing chamber from thefirst auxiliary vacuum chamber; second wafer transfer means fortransferring the wafer to the second auxiliary vacuum chamber from thevacuum processing chamber; driving means for driving the first andsecond wafer transfer means in a mutually synchronized manner; wafercassette supporting means for supporting a cassette contacting aplurality of wafers; and wafer transport means for transporting thewafer into the first auxiliary vacuum chamber from the cassette one byone; in which said first wafer transfer means comprises a first waferplaten for supporting a wafer, a first sealing gate, and a firstelevating unit controllable for selectively raising and lowering saidfirst wafer platen and said first sealing gate together, said firstsealing gate establishing a sealing condition when raised to anuppermost position thereof, in which said first auxiliary vacuum chamberis hermetically sealed with respect to said vacuum processing chamber,and in which said second wafer transfer means comprises a second waferplaten for supporting a wafer, a second sealing gate, and a secondelevating unit controllable for selectively raising and lowering saidsecond wafer platen and said second sealing gate together, said secondsealing gate establishing a sealing condition when raised to anuppermost position thereof, in which said second auxiliary vacuumchamber is hermetically sealed with respect to said vacuum processingchamber.
 5. An ion implantation apparatus, comprising:a vacuumprocessing chamber in which a wafer is subjected to ion implantationprocessing; first and second auxiliary vacuum chambers each of which ishermetically sealable from or connectable to the outer atmosphere andvacuum processing chamber, and each of which is constructed totemporarily store the wafer; first gate means which is hermeticallysealable between the vacuum processing chamber and the first auxiliaryvacuum chamber; second gate means which is hermetically sealable betweenthe vacuum processing chamber and the second auxiliary vacuum chamber;first wafer transfer means for transferring a wafer into the vacuumprocessing chamber from the first auxiliary vacuum chamber through thefirst gate means; second wafer transfer means for transferring the waferto the second auxiliary vacuum chamber from the vacuum processingchamber through the second gage means; driving means for driving thefirst and second wafer transfer means; wafer cassette supporting meansfor supporting a cassette containing a plurality of wafers; and wafertransport means for transporting the wafer into the first auxiliaryvacuum chamber from the cassette one by one; wherein said first gatemeans includes a first gate provided in the first auxiliary vacuumchamber and movable to seal and connect between the first auxiliaryvacuum chamber and the vacuum processing chamber, the first gatesupporting one wafer to be subjected to ion implantation processing, andsaid second gate means includes a second gate provided in the secondauxiliary vacuum chamber and movable to seal and connect between thesecond auxiliary vacuum chamber and the vacuum processing chamber, thesecond gate supporting one wafer which has been subjected to ionimplantation processing.
 6. An ion implantation apparatus comprising:avacuum processing chamber in which a wafer is subjected to ionimplantation processing; first and second auxiliary vacuum chambers eachof which is hermetically sealable from or connectable to the outeratmosphere and vacuum processing chamber, and each of which isconstructed to temporarily store the wafer; first gate means which ishermetically sealable between the vacuum processing chamber and thefirst auxiliary vacuum chamber; second gate means which is hermeticallysealable between the vacuum processing chamber and the second auxiliaryvacuum chamber; first wafer transfer means for transferring a wafer intothe vacuum processing chamber from the first auxiliary vacuum chamberthrough the first gate means; second wafer transfer means fortransferring the wafer to the second auxiliary vacuum chamber from thevacuum processing chamber through the second gate means; driving meansfor driving the first and second wafer transfer means; wafer cassettesupporting means for supporting a cassette containing a plurality ofwafers; and wafer transport means for transporting the wafer into thefirst auxiliary vacuum chamber from the cassette one by one; said firstwafer transfer means including first and second arms; said second wafertransfer means including third and fourth arms; said driving meansmoving said first and second arms so that a first wafer becomes retainedtherebetween and moves said third and fourth arms so that a second waferbecomes retained therebetween; wherein said first and third arms arefixedly connected to said first wafer transfer means and said second andfourth arms are fixedly connected to said second wafer transfer means,said driving means being operable to selectively; (a) drive said firstand second wafer retaining members in first mutually oppositedirections, for retaining said first wafer between said first and secondarms and retaining said second wafer between said third and fourth arms;(b) drive said first and second wafer retaining members together along aspecific direction, for transferring one of said first and second wafersfrom said first auxiliary vacuum chamber to said vacuum processingchamber while transferring the other wafer of said first and secondwafers from said vacuum processing chamber to said second auxiliaryvacuum chamber; (c) drive said first and second wafer retaining membersin second mutually opposite directions, for releasing said first waferfrom between said first and second arms and releasing said second waferfrom between said third and fourth arms; and (c) drive said first andsecond wafer retaining members together in the opposite direction tosaid specific direction.
 7. An ion implantation apparatus, comprising:avacuum processing chamber in which a wafer is subjected to ionimplantation processing; first and second auxiliary vacuum chambers eachof which is hermetically sealable from or connectable to the outeratmosphere and vacuum processing chamber, and each of which isconstructed to temporarily store the wafer; first gate means which ishermetically sealable between the vacuum processing chamber and thefirst auxiliary vacuum chamber; second gate means which is hermeticallysealable between the vacuum processing chamber and the second auxiliaryvacuum chamber; first wafer transfer means for transferring a wafer intothe vacuum processing chamber from the first auxiliary vacuum chamberthrough the first gate means; second wafer transfer means fortransferring the wafer to the second auxiliary vacuum chamber from thevacuum processing chamber through the second gate means; driving meansfor driving the first and second wafer transfer means; wafer cassettesupporting means for supporting a cassette containing a plurality ofwafers; and wafer transport means for transporting the wafer into thefirst auxiliary vacuum chamber from the cassette one by one; in whichsaid first wafer transfer means comprises a first wafer platen forsupporting a wafer, and a first elevating unit controllable forselectively raising and lowering said first wafer platen and said firstgate together, said first gate establishing a sealing condition whenraised to an uppermost position thereof, in which said first auxiliaryvacuum chamber is hermetically sealed with respect to said vacuumprocessing chamber, and in which said second wafer transfer meanscomprises a second wafer platen for supporting a wafer, and a secondelevating unit controllable for selectively raising and lowering saidsecond wafer platen and said second gate together, said second gateestablishing a sealing condition when raised to an uppermost positionthereof, in which said second auxiliary vacuum chamber is hermeticallysealed with respect to said vacuum processing chamber.
 8. An ionimplantation apparatus, comprising:a vacuum processing chamber in whicha wafer is subjected to ion implantation processing; first and secondauxiliary vacuum chambers each of which is hermetically sealable from orconnectable to the outer atmosphere and vacuum processing chamber, andeach of which is constructed to temporarily store the wafer; first wafertransfer means for transferring a wafer into the chamber processingchamber from the first auxiliary vacuum chamber; second wafer transfermeans for transferring the wafer to the second auxiliary vacuum chamberfrom the vacuum processing chamber; driving means for driving the firstand second wafer transfer means in a mutually synchronized manner; wafercassette supporting means for supporting a cassette containing aplurality of wafers; and first and second wafer transport means providedoutside the vacuum processing chamber and auxiliary vacuum chambers, thefirst wafer transport means transporting the wafer to be subject to ionimplantation processing to the second transport means from the cassette,and the wafer which has been subjected to ion implantation processing tothe cassette from the second auxiliary vacuum chamber, and said secondtransport means transporting the wafer into the first auxiliary vacuumchamber from the first wafer transport means.
 9. The apparatus accordingto claim 8, wherein:said first wafer transfer means includes first andsecond arms; said second wafer transfer means includes third and fourtharms; and said driving means moves said first and second arms so that afirst wafer becomes retained therebetween and moves said third andfourth arms so that a second wafer becomes retained therebetween. 10.The apparatus according to claim 9, wherein said first and third armsare fixedly connected to said first wafer transfer means and said secondand fourth arms are fixedly connected to said second wafer transfermeans, said driving means being operable to selectively:(a) drive saidfirst and second wafer retaining members in first mutually oppositedirections, for retaining said first wafer between said first and secondarms and retaining said second wafer between said third and fourth arms;(b) drive said first and second wafer retaining members together along aspecific direction, for transferring one of said first and second wafersfrom said first auxiliary vacuum chamber to said vacuum processingchamber while transferring the other wafer of said first and secondwafers from said vacuum processing chamber to said second auxiliaryvacuum chamber; (c) drive said first and second wafer retaining membersin second mutually opposite directions, for releasing said first waferfrom between said first and second arms and releasing said second waferfrom between said third and fourth arms; and (d) drive said first andsecond wafer retaining members together in the opposite direction tosaid specific direction.
 11. The apparatus according to claim 8 in whichsaid first wafer transfer means comprises a first wafer platen forsupporting a wafer, a first sealing gate, and a first elevating unitcontrollable for selectively raising and lowering said first waferplaten and said first sealing gate together, said first sealing gateestablishing a sealing condition when raised to an uppermost positionthereof, in which said first auxiliary vacuum chamber is hermeticallysealed with respect to said vacuum processing chamber, andin which saidsecond wafer transfer means comprises a second wafer platen forsupporting a wafer, a second sealing gate, and a second elevating unitcontrollable for selectively raising and lowering said second waferplaten and said second sealing gate together, said second sealing gateestablishing a sealing condition when raised to an uppermost positionthereof, in which said second auxiliary vacuum chamber is hermeticallysealed with respect to said vacuum processing chamber.
 12. The apparatusaccording to claim 8, wherein:said wafer cassette supporting meansincludes elevating means for controlling the vertical height of saidwafer cassette; said wafer transport means includes a first wafercarrier member formed to receive and support a wafer, and first drivemeans for rotating said first wafer carrier member about a first fixedaxis and for moving said first wafer carrier member outward and inwardwith respect to said first fixed axis; said second wafer transport unitincludes a second wafer carrier member formed to receive and support awafer, and second drive means for rotating said second wafer carriermember about a second fixed axis and for moving said second wafercarrier member outward and inward with respect to said second fixedaxis; said ion implantation apparatus further comprising a waferalignment means adapted to support a wafer and including means fordetecting a position of a wafer supported thereon and for rotating saidwafer into a specific position based on said detection.
 13. An ionimplantation apparatus, comprising:a vacuum processing chamber in whicha wafer is subjected to ion implantation processing; first and secondvacuum chambers each of which is hermetically sealable from orconnectable to the outer atmosphere and vacuum processing chamber, andeach of which is constructed to temporarily store the wafer; first wafertransfer means for transferring a wafer into the vacuum processingchamber from the first auxiliary vacuum chamber; second wafer transfermeans for transferring the wafer to the second auxiliary vacuum chamberfrom the vacuum processing chamber; driving means connected to the firstand second wafer transfer means for driving the first and second wafertransfer means in a mutually synchronized manner so that two wafers aresimultaneously transferred to the vacuum processing chamber and secondauxiliary vacuum chamber from the first auxiliary vacuum chamber andvacuum processing chamber; said first wafer transfer means includingfirst and second arms, said second wafer transfer means including thirdand fourth arms, and said driving means including a first retainingmember connecting the first and third arms together, and a secondretaining member connecting the second and fourth arms together.